Total Indicator Runout (TIR), or the reference value of how much a tool moves (or wobbles) off center as it rotates, is measured by setting up a part so that it rotates about a particular axis, then measuring a surface of interest as the part is rotated. The difference between the two most extreme measurements of the indicator from anywhere on that surface is the TIR.
When it comes to toolholding systems, 3 microns or less of TIR is ideal. High-precision toolholding systems, if properly maintained and assembled, likely are able to provide assembled TIR in the 3- to 5-micron range. Toolholding systems are able to help hold low TIR throughout many years of service while providing vibration damping, strength and rigidity. This results in a shop’s ability to boost speeds and feeds and metal-removal rates, increase tool life, accuracy and quality of finish, and realize lower cost per part leading to wider margins. Poor TIR results in significant tool wear or failure and increased cost per part because of the need to replace cutting tools or add operations.
There are a few options available when it comes to measuring TIR.
Tool presetters are commonly used to identify a reference TIR, according to REGO-FIX Engineering & Technical Manager David McHenry. They do so by measuring a tool’s cutting edges to assure they precisely match job specifications and are ready to be used in a tool machine.
“Say you’re using a steep taper toolholder, for example, and a CAT 40 toolholder, you can measure it in several different ways. For example, you can use a high-end presetter to obtain a reference TIR, and I call it a reference TIR because the presetter itself has a spindle which has runout in it, and an adapter, usually to bring it down to that taper size. And that adapter has a runout or tolerance fit, so it’s a good reference point to let you know whether your tool is good or bad.”
Another way to measure TIR is with a zero spindle. Zero spindles inspect concentricity, squareness, roundness and diameter, are made for a particular toolholder and, because of their bearings, allow an operator to compensate and dial it in.
Magnetic v-blocks are another way to measure TIR. A magnetic v-block does not have any metal bearings at all and is actually a metal-to-metal contact. The sides, base, and contact surface must be precision ground so that the work piece can have reliable and repeatable reference surfaces on which to machine the work piece. Although v-blocks allow you to truly measure the runout of the assembly, this method does have its risks: It requires a very good operator and the tool can be marked or scratched.
Another option, though not preferred, is stopping your machine spindle, loading a toolholder, then measuring it in the spindle.
“The last thing you really want to do is to have your machine not making chips just so you can measure the runout,” said McHenry. “Although there are cases when you have to do it this way, overall it’s not ideal.”
McHenry says that every customer needs to find a solution that works for them. Whether it’s using an expensive presetter or one that’s been on the shop floor forever, a zero spindle or magnetic v-block, shops need to know what they’re using and its limitations, whether it’s providing a reference value or real value, and then how that will translate when making parts.